It’s normal, in rough sea the ship is following waves height...and can be meters too high in regard of your torp at the impact instant.
Best is to set torp depth quite high to counter this.
Keep in mind your torp is running straight without following waves...the ship is following waves!
On side note, using Hsie torpedo fix option, torp can be way off too low (quite often in fact - too often to me, that’s why i don’t use this option)
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